The truths about low E reflective insulations.

[fastline12]

Looking to build another shop for our company and a couple designers are highly recommending some low emissivity reflective wrap products to capture between our metal corrugated sheeting and our frame structure. While I do not doubt the usefulness of the product, I am kind of calling BS to the claimed R15.5 for a product that is .25" thick.. This is a touch outside my area of expertise but as I understand it, R values cannot be directly calculated with wraps like this and the best stuff I have seen might achieve an R7 for this thickness but cost WAY outside out budget.

Obviously we are looking for insulation for our building. We plan to also add 8" glass batts on the interior so really trying to gauge the effectiveness of a product like this in use.

 

[MintJulep]

Simple. When the designer comes to you with his performance claims you say "Please show me objective evidence to document your insulation system performance claims in the form of a test report from a recognized independent laboratory showing the performance of the insulation system you are proposing when tested to ASTM C1363."

 

[moltenmetal]

We're talking about the aluminized bubble wrap here, right?

Radiant barriers only work if there is an air gap (or better still a vacuum) between the reflective surface and the surface experiencing the high temperature. Sandwiching this barrier between anything in a wall construction is going to give it greatly reduced effectiveness.

As a replacement for batts, or to reduce thickness of batts? Absolutely not. As an expensive supplementary insulation? Well, I guess that depends on how much you trust their testing. Did they test in the configuration they're making the R value claim? Doubtful.

 

[davefitz]

It may have its uses, particularly if the hot surface is directly above the bubble wrap, such as with crawlspaces ( under floor) or under a hot steel roof. I've seen lab reports indicating an equivalent R of 15.5 - 17 in that configuration, but much lower values in a vertical wall configuration.

In using the buble warap in crawlspace applications one can avoid the common problems one has with fiberglass insulation such as damp humid soaking of the fiberglass , but there may be issues of electrical conductivity and also water permiability.

 

[fastline12]

Thanks for the replies. As mentioned, the product would be installed between the corrugated metal and the studs. The sheeting has raised ribs for added stiffness that are about 1.25' tall so that area does create an air gap which "might" improve performance or at least approach the ratings.

The product is basically Al sheet on both sides of a polyethylene sheet. From what I have gathered, the product would drastically lose effectiveness in a building if it is further insulated with batts. I tend to agree that the roof would probably be the only place I would try it. There would be a LARGE heating load up there in which any radiant rejection would be welcome.

The designers were recommending the product as a stand alone product and from what I found, it works best by itself and loses effectiveness with additional insulation.